One particular type of light fixture is known as a lay-in luminaire, or a troffer. The lensed troffer is the most popular lay-in sold today. It is a commodity that is sold for use in applications where price is the primary buying consideration. For many decades, the recessed parabolic was the standard for high performance applications such as offices. The “parabolic” style troffer utilizes aluminum baffles to shield the light and maximize high angle shielding while sacrificing light on the walls. In recent years, the market has been moving away from the parabolics towards troffers with broader distributions for high performance applications.
A troffer is typically installed within a suspended ceiling grid system where one or more ceiling tiles are replaced with the troffer. Thus, the exterior dimensions of the troffer are typically sized to fit within the regular spacing of the ceiling tiles. In the United States, the spacing of the ceiling grid is often 2 foot (61 cm) by 2 foot (61 cm) and, therefore, troffers will typically have a dimension that is a multiple of 2 feet (61 cm). For example, many troffers are 2′ (61 cm)×2′ (61 cm) or 2′ (61 cm)×4′ (122 cm). Similar regular spacing is also provided in Europe but is provided in a metric unit of measure.
Conventional approaches to providing solid state lighting in a suspended ceiling grid system have included replacing fluorescent tubes with an LED lamp that directly replaced the tube. Such an approach utilized existing fluorescent troffer fixtures and replaced just the lamp.
Another approach to providing solid state lighting for a suspended ceiling grid system has been to provide an illuminated panel that is substantially coplanar with the ceiling tiles. Still other approaches have provided a solid state lighting luminaire that looks similar to a lensed troffer with a macro level lensed sheet being provided between the solid state light sources and the room.
A challenge with solid state light emitters is that many solid state light emitters do not operate well in high temperatures. For example, many LED light sources have average operating lifetimes of decades as opposed to just months or 1-2 years for many incandescent bulbs, but some LEDs' lifetimes can be significantly shortened if they are operated at elevated temperatures. It is generally accepted that the junction temperature of an LED should not exceed 70 degrees C. if a long lifetime is desired. In addition, some LEDs (e.g., those that emit red light) have a very strong temperature dependence. AlInGaP LEDs can reduce in optical output by ˜25% when heated up by ˜40° C.
A further challenge with solid state lighting arises from the relatively high light output from a relatively small area provided by solid state emitters. Such a concentration of light output may present challenges in providing solid state lighting systems for general illumination in that, in general, large changes in brightness in a small area may be perceived as glare and distracting to occupants.
Yet another challenge with providing a solid state lighting system for troffer application relates to the distance the luminaire may extend above the ceiling tile. While the area above a suspended ceiling may in many cases be quite deep, in some applications there may be obstructions or other constraints that limit the distance above the ceiling which the luminaire may extend. For example, in some applications the luminaire may not extend more than 5 inches (12.7 cm) above the ceiling tile. Such restriction in height may present difficulties in providing luminaires with a high shield angle, as such shield angles are typically provided by recessing the light source into the ceiling.